2
The wrong material
Workbook 2: Topic 3.3, pp. 35–37
GoalSay why a material is a poor choice for a job.
New words
poor choice · not a good material for the jobbreak · to come apart in piecessoggy · wet and soft
Explanation
Some materials are the wrong choice for a job. A bucket made of paper would go soggy and leak. A spoon made of wool would bend and could not lift soup. A bridge made of tissue would break. A window made of wood would not let light in. To check a choice, ask: what property does this job need? Does the material have it? If the answer is no, we need a different material.
| Object | Wrong material | Why it does not work |
|---|---|---|
| bucket | paper | it goes soggy |
| spoon | wool | it bends too much |
| window | wood | you cannot see through it |
Worked examples
Tom’s sock is made of glass. It would be hard and it would break. Wool is better because it is soft and flexible.
A chair made of sponge would be too soft to hold a person. Wood is better because it is strong and rigid.
An umbrella made of paper would get wet through and fall apart. Plastic or waterproof fabric keeps us dry.
Class activity
Silly object game (with an adult): think of a silly object, such as a paper cup for hot tea or a metal sock. One person says the silly object, the other says which property is missing and chooses a better material.
Practice
1
Why is a plastic bag a good material for carrying wet things?
Because it is waterproof.
2
Mia makes a cup from tissue paper. What goes wrong?
Tissue paper is absorbent and weak, so the cup goes soggy and leaks.
3
Choose a better material for a spoon: wool or metal?
B, metal. It is strong and rigid.
4
A window needs to be transparent. Is wood a good choice?
No. You cannot see through wood.